Can't see object in weight paint mode
Maybe you have some modifiers on your mesh, such as "Mirror modifier", "skin modifier", "sub surface", etc.
Just apply those modifiers, check if they got out from the hierarchy on the right tab under your mesh.
Then select your mesh and your armature and go to pose mode: from there select Parent > Automatic weight > Automatic weight.
You should be able to see the weight on your mesh then.
Good work and have a nice day.